The transmission of diseases and damage to man-made structures as well as crops by birds is well known and documented. Substances that are obnoxious, offensive, repugnant, revulsive or otherwise repulsive to birds have been known for a number of years. Some of these substances have been tried, with varying degrees of success, as bird repellents on assorted crops, feeds and surfaces.
U.S. Pat. No. 2,967,128 to Kare discloses a number of derivatives of anthranilic acid esters and esters of phenyl acetic acid which are proposed as taste repellents for birds. U.S. Pat. No. 4,790,990 to Mason et al. (which lists Kare as a coinventor) discloses a combination that encapsulates these repellents in starch matrices that are then added to livestock feed to reduce its consumption by birds.
The preferred repellents disclosed by Kare are water insoluble dimethyl anthranilate, methyl anthranilate, ethyl anthranilate, phenyl ethyl anthranilate, menthyl anthranilate, and dimethyl benzyl carbonyl acetate. Kare proposes the dispersal of these repellents by using organic solvents and liquid or solid carriers. The Mason et al. disclosure is directed to partial entrapment of the repellents in edible solid vehicles, such as modified food starches.
A number of serious problems have been encountered in attempted experiments following the disclosed information provided by the Kare patent. They would preclude the use and application of these repellents to agricultural crops. These include the continued insolubility of the active ingredients in water, their toxicity to plants (phytotoxicity), their extremely short life span under sunlight, and the attractiveness of these chemical agents to insects.
The insolubility of dimethyl and methyl anthranilate in water was the first major problem encountered. When combined with the solvents and synthetic surfactants described in the patent neither dimethyl or methyl anthranilate, the two most common anthranilic derivatives available for commercial use, remained soluble when mixed with water, which is the preferred medium for commercial applications of pesticides. Large quantities of one or two gallons of these pesticides were difficult to combine with two or four hundred gallons of water in commercial sprayers. The anthranilic oils would either separate into globules, form a film on the water surface, adhere to the walls of the metal tanks or destroy the plastic hoses. Precipitates quickly formed once agitation was stopped and were difficult to reincorporate into the water. When applied to a crop, spots of anthranilic oil were left on the plant surfaces rather than forming an even protective coating.
Plant toxicity (phytotoxicity) with both dimethyl and methyl anthranilate were immediately noted in experimental efforts using materials and techniques that followed the Kare disclosures. This is not in itself surprising, since these chemicals have recognized herbicidal properties. Brown spots appeared within twenty minutes after application where either of the anthranilates touched the leaf or fruit surfaces at 2500 parts per million (ppm) concentration rates. All of the leaves and plants on the plants immediately turned brown when the application rate was doubled. Tests conducted to determine the upper ranges of phytotoxicity indicated that the concentration limits for the repellents were far below that needed to repel birds from the tested crops.
The efficacy of both dimethyl and methyl anthranilate in reducing bird depredation of crops, as described by Kare, was also observed to be limited. Birds, when observed in confinement and in the field, readily returned to the crop or food source on the fourth day after application. It was hypothesized that the characteristic odor or flavor, associated with either compound, was not detected by the birds.
A series of tests were developed to prove this theory. In the first experiment, conducted under laboratory conditions, the results indicated that the compounds decompose within sixty-four hours when exposed to ultraviolet light. Moreover, the addition of solvents increased the volatility of the anthranilates and, in some cases, may have contributed to the phytotoxic properties. Some organic solvents can also be toxic to humans and animals feeding on the harvested treated crops.
In an experiment designed to separate the effects of ultraviolet light from the light spectrum and to assess its impact on the anthranilates, a series of petri dishes containing either methyl anthranilate or methyl anthranilate combined with potassium salts of fatty acids were placed in the out-of-doors. The results showed unequivocally that ultraviolet light is the primary factor that causes the methyl anthranilate to lose its primary odor and taste repellent properties.
The research leading to this disclosure showed that the addition of anionic surfactants or emulsifiers, such as alkyl metal salts of fatty acids or naturally occurring soaps, alleviates this problem of low solubility in water. This is accomplished by forming a consistent emulsion that suspends the repellent in an aqueous solution without separation or precipitation during the application process.
By combining them with natural soaps, the acceptable upper range of concentration of the active repellents was increased by a factor of 15 to 65 on the plants tested. Furthermore this addition greatly extended the life of the repellent properties of the compositions by 150%, to a total of ten days.
The use of encapsulation, as disclosed by the Mason et al. patent, was explored but discarded. Encapsulation eliminates volatility, an important discovery of this patent disclosure. It also precludes the adhesion of either dimethyl or methyl anthranilate directly to the surface of the object to be protected unless additional adhesive agents are added to the formulation. Use of adhesive agents is an alternative which is cost prohibitive for commercial applications of these repellents.
In experiments developed to determine the response of birds to dimethyl and methyl anthranilate treated fruits, grains, water, perches and nests it was discovered that the fragrances or aromas may be more repulsive than taste. Birds presented with both treated and untreated fruits, grains and water for the first time initially fed or drank from both for a short period, generally less than two minutes, before abandoning the treated samples. When reintroduced in reverse order the birds refused to touch the treated materials even though they had not fed or drank from the containers for several hours. The addition of untreated food on suspended screens above the treated materials, elicited the same results. No foods were eaten as long as the anthranilic odors could be detected by the birds. Birds would also not return to perches treated with the compounds until the odor of the active repellents had dissipated.
It was also discovered that insects are readily attracted to dimethyl and methyl anthranilate. Crops relatively free of insects were quickly reinfested after being treated with either material. The addition of soaps, however, reduced this problem.
Bird repellents designed to reduce depredation over a large area must be applied in an aqueous medium with power assisted equipment. Dimethyl and methyl anthranilate, to this point, have required that they be solubilized with organic solvents and emulsifiers or surfactants before they are placed in an aqueous medium. This, in turn, has created further dispensing problems. Distribution is difficult because the repellents agglomerate as globules or precipitate within the aqueous medium used as the dispensing agent. The resulting concentration of the repellent leaves an uneven layer of repellent on treated surfaces and can discolor, burn and kill treated plants. Experimental treatments of dimethyl and methyl anthranilates on cherries, blueberries and grapes, resulted in spotty coverage and serious plant injury. The repellents attracted unwanted insects and required repeated applications every four to five days to be effective. Application with the unique formulations, herein described, greatly enhanced the repellency characteristics of the anthranilates.
This invention discloses a novel formulation that eliminates or reduces the above described problems. The combination of materials disclosed herein produces a uniform application solution, extends the useful life of the repellent, eliminates plant phytotoxicity within prescribed application rates, and reduces insect reinfestations.
The use of certain fatty acids as biodegradable insecticides is well-known in the literature. For example, U.S. Pat. No. 4,870,102 to Puritch et al. describes a composition and method of killing mites with a mixture of salts of fatty acids and alcohol.